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1/* vi: set sw=4 ts=4: */
2/*
3 * bare bones sendmail
4 *
5 * Copyright (C) 2008 by Vladimir Dronnikov <dronnikov@gmail.com>
6 *
7 * Licensed under GPLv2, see file LICENSE in this source tree.
8 */
9//config:config SENDMAIL
10//config: bool "sendmail"
11//config: default y
12//config: help
13//config: Barebones sendmail.
14
15//applet:IF_SENDMAIL(APPLET(sendmail, BB_DIR_USR_SBIN, BB_SUID_DROP))
16
17//kbuild:lib-$(CONFIG_SENDMAIL) += sendmail.o mail.o
18
19//usage:#define sendmail_trivial_usage
20//usage: "[-tv] [-f SENDER] [-amLOGIN 4<user_pass.txt | -auUSER -apPASS]"
21//usage: "\n [-w SECS] [-H 'PROG ARGS' | -S HOST] [RECIPIENT_EMAIL]..."
22//usage:#define sendmail_full_usage "\n\n"
23//usage: "Read email from stdin and send it\n"
24//usage: "\nStandard options:"
25//usage: "\n -t Read additional recipients from message body"
26//usage: "\n -f SENDER For use in MAIL FROM:<sender>. Can be empty string"
27//usage: "\n Default: -auUSER, or username of current UID"
28//usage: "\n -o OPTIONS Various options. -oi implied, others are ignored"
29//usage: "\n -i -oi synonym, implied and ignored"
30//usage: "\n"
31//usage: "\nBusybox specific options:"
32//usage: "\n -v Verbose"
33//usage: "\n -w SECS Network timeout"
34//usage: "\n -H 'PROG ARGS' Run connection helper. Examples:"
35//usage: "\n openssl s_client -quiet -tls1 -starttls smtp -connect smtp.gmail.com:25"
36//usage: "\n openssl s_client -quiet -tls1 -connect smtp.gmail.com:465"
37//usage: "\n $SMTP_ANTISPAM_DELAY: seconds to wait after helper connect"
38//usage: "\n -S HOST[:PORT] Server (default $SMTPHOST or 127.0.0.1)"
39//usage: "\n -amLOGIN Log in using AUTH LOGIN (-amCRAM-MD5 not supported)"
40//usage: "\n -auUSER Username for AUTH"
41//usage: "\n -apPASS Password for AUTH"
42//usage: "\n"
43//usage: "\nIf no -a options are given, authentication is not done."
44//usage: "\nIf -amLOGIN is given but no -au/-ap, user/password is read from fd #4."
45//usage: "\nOther options are silently ignored; -oi is implied."
46//usage: IF_MAKEMIME(
47//usage: "\nUse makemime to create emails with attachments."
48//usage: )
49
50/* Currently we don't sanitize or escape user-supplied SENDER and RECIPIENT_EMAILs.
51 * We may need to do so. For one, '.' in usernames seems to require escaping!
52 *
53 * From http://cr.yp.to/smtp/address.html:
54 *
55 * SMTP offers three ways to encode a character inside an address:
56 *
57 * "safe": the character, if it is not <>()[].,;:@, backslash,
58 * double-quote, space, or an ASCII control character;
59 * "quoted": the character, if it is not \012, \015, backslash,
60 * or double-quote; or
61 * "slashed": backslash followed by the character.
62 *
63 * An encoded box part is either (1) a sequence of one or more slashed
64 * or safe characters or (2) a double quote, a sequence of zero or more
65 * slashed or quoted characters, and a double quote. It represents
66 * the concatenation of the characters encoded inside it.
67 *
68 * For example, the encoded box parts
69 * angels
70 * \a\n\g\e\l\s
71 * "\a\n\g\e\l\s"
72 * "angels"
73 * "ang\els"
74 * all represent the 6-byte string "angels", and the encoded box parts
75 * a\,comma
76 * \a\,\c\o\m\m\a
77 * "a,comma"
78 * all represent the 7-byte string "a,comma".
79 *
80 * An encoded address contains
81 * the byte <;
82 * optionally, a route followed by a colon;
83 * an encoded box part, the byte @, and a domain; and
84 * the byte >.
85 *
86 * It represents an Internet mail address, given by concatenating
87 * the string represented by the encoded box part, the byte @,
88 * and the domain. For example, the encoded addresses
89 * <God@heaven.af.mil>
90 * <\God@heaven.af.mil>
91 * <"God"@heaven.af.mil>
92 * <@gateway.af.mil,@uucp.local:"\G\o\d"@heaven.af.mil>
93 * all represent the Internet mail address "God@heaven.af.mil".
94 */
95
96#include "libbb.h"
97#include "mail.h"
98
99// limit maximum allowed number of headers to prevent overflows.
100// set to 0 to not limit
101#define MAX_HEADERS 256
102
103static void send_r_n(const char *s)
104{
105 if (verbose)
106 bb_error_msg("send:'%s'", s);
107 printf("%s\r\n", s);
108}
109
110static int smtp_checkp(const char *fmt, const char *param, int code)
111{
112 char *answer;
113 char *msg = send_mail_command(fmt, param);
114 // read stdin
115 // if the string has a form NNN- -- read next string. E.g. EHLO response
116 // parse first bytes to a number
117 // if code = -1 then just return this number
118 // if code != -1 then checks whether the number equals the code
119 // if not equal -> die saying msg
120 while ((answer = xmalloc_fgetline(stdin)) != NULL) {
121 if (verbose)
122 bb_error_msg("recv:'%.*s'", (int)(strchrnul(answer, '\r') - answer), answer);
123 if (strlen(answer) <= 3 || '-' != answer[3])
124 break;
125 free(answer);
126 }
127 if (answer) {
128 int n = atoi(answer);
129 if (timeout)
130 alarm(0);
131 free(answer);
132 if (-1 == code || n == code) {
133 free(msg);
134 return n;
135 }
136 }
137 bb_error_msg_and_die("%s failed", msg);
138}
139
140static int smtp_check(const char *fmt, int code)
141{
142 return smtp_checkp(fmt, NULL, code);
143}
144
145// strip argument of bad chars
146static char *sane_address(char *str)
147{
148 char *s;
149
150 trim(str);
151 s = str;
152 while (*s) {
153 if (!isalnum(*s) && !strchr("_-.@", *s)) {
154 bb_error_msg("bad address '%s'", str);
155 /* returning "": */
156 str[0] = '\0';
157 return str;
158 }
159 s++;
160 }
161 return str;
162}
163
164// check for an address inside angle brackets, if not found fall back to normal
165static char *angle_address(char *str)
166{
167 char *s, *e;
168
169 trim(str);
170 e = last_char_is(str, '>');
171 if (e) {
172 s = strrchr(str, '<');
173 if (s) {
174 *e = '\0';
175 str = s + 1;
176 }
177 }
178 return sane_address(str);
179}
180
181static void rcptto(const char *s)
182{
183 if (!*s)
184 return;
185 // N.B. we don't die if recipient is rejected, for the other recipients may be accepted
186 if (250 != smtp_checkp("RCPT TO:<%s>", s, -1))
187 bb_error_msg("Bad recipient: <%s>", s);
188}
189
190// send to a list of comma separated addresses
191static void rcptto_list(const char *list)
192{
193 char *str = xstrdup(list);
194 char *s = str;
195 char prev = 0;
196 int in_quote = 0;
197
198 while (*s) {
199 char ch = *s++;
200
201 if (ch == '"' && prev != '\\') {
202 in_quote = !in_quote;
203 } else if (!in_quote && ch == ',') {
204 s[-1] = '\0';
205 rcptto(angle_address(str));
206 str = s;
207 }
208 prev = ch;
209 }
210 if (prev != ',')
211 rcptto(angle_address(str));
212 free(str);
213}
214
215int sendmail_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
216int sendmail_main(int argc UNUSED_PARAM, char **argv)
217{
218 char *opt_connect;
219 char *opt_from = NULL;
220 char *s;
221 llist_t *list = NULL;
222 char *host = sane_address(safe_gethostname());
223 unsigned nheaders = 0;
224 int code;
225 enum {
226 HDR_OTHER = 0,
227 HDR_TOCC,
228 HDR_BCC,
229 } last_hdr = 0;
230 int check_hdr;
231 int has_to = 0;
232
233 enum {
234 //--- standard options
235 OPT_t = 1 << 0, // read message for recipients, append them to those on cmdline
236 OPT_f = 1 << 1, // sender address
237 OPT_o = 1 << 2, // various options. -oi IMPLIED! others are IGNORED!
238 OPT_i = 1 << 3, // IMPLIED!
239 //--- BB specific options
240 OPT_w = 1 << 4, // network timeout
241 OPT_H = 1 << 5, // use external connection helper
242 OPT_S = 1 << 6, // specify connection string
243 OPT_a = 1 << 7, // authentication tokens
244 OPT_v = 1 << 8, // verbosity
245 };
246
247 // init global variables
248 INIT_G();
249
250 // default HOST[:PORT] is $SMTPHOST, or localhost
251 opt_connect = getenv("SMTPHOST");
252 if (!opt_connect)
253 opt_connect = (char *)"127.0.0.1";
254
255 // save initial stdin since body is piped!
256 xdup2(STDIN_FILENO, 3);
257 G.fp0 = xfdopen_for_read(3);
258
259 // parse options
260 // -v is a counter, -H and -S are mutually exclusive, -a is a list
261 opt_complementary = "vv:H--S:S--H";
262 // N.B. since -H and -S are mutually exclusive they do not interfere in opt_connect
263 // -a is for ssmtp (http://downloads.openwrt.org/people/nico/man/man8/ssmtp.8.html) compatibility,
264 // it is still under development.
265 opts = getopt32(argv, "tf:o:iw:+H:S:a:*:v", &opt_from, NULL,
266 &timeout, &opt_connect, &opt_connect, &list, &verbose);
267 //argc -= optind;
268 argv += optind;
269
270 // process -a[upm]<token> options
271 if ((opts & OPT_a) && !list)
272 bb_show_usage();
273 while (list) {
274 char *a = (char *) llist_pop(&list);
275 if ('u' == a[0])
276 G.user = xstrdup(a+1);
277 if ('p' == a[0])
278 G.pass = xstrdup(a+1);
279 // N.B. we support only AUTH LOGIN so far
280 //if ('m' == a[0])
281 // G.method = xstrdup(a+1);
282 }
283 // N.B. list == NULL here
284 //bb_error_msg("OPT[%x] AU[%s], AP[%s], AM[%s], ARGV[%s]", opts, au, ap, am, *argv);
285
286 // connect to server
287
288 // connection helper ordered? ->
289 if (opts & OPT_H) {
290 const char *delay;
291 const char *args[] = { "sh", "-c", opt_connect, NULL };
292 // plug it in
293 launch_helper(args);
294 // Now:
295 // our stdout will go to helper's stdin,
296 // helper's stdout will be available on our stdin.
297
298 // Wait for initial server message.
299 // If helper (such as openssl) invokes STARTTLS, the initial 220
300 // is swallowed by helper (and not repeated after TLS is initiated).
301 // We will send NOOP cmd to server and check the response.
302 // We should get 220+250 on plain connection, 250 on STARTTLSed session.
303 //
304 // The problem here is some servers delay initial 220 message,
305 // and consider client to be a spammer if it starts sending cmds
306 // before 220 reached it. The code below is unsafe in this regard:
307 // in non-STARTTLSed case, we potentially send NOOP before 220
308 // is sent by server.
309 //
310 // If $SMTP_ANTISPAM_DELAY is set, we pause before sending NOOP.
311 //
312 delay = getenv("SMTP_ANTISPAM_DELAY");
313 if (delay)
314 sleep(atoi(delay));
315 code = smtp_check("NOOP", -1);
316 if (code == 220)
317 // we got 220 - this is not STARTTLSed connection,
318 // eat 250 response to our NOOP
319 smtp_check(NULL, 250);
320 else
321 if (code != 250)
322 bb_error_msg_and_die("SMTP init failed");
323 } else {
324 // vanilla connection
325 int fd;
326 fd = create_and_connect_stream_or_die(opt_connect, 25);
327 // and make ourselves a simple IO filter
328 xmove_fd(fd, STDIN_FILENO);
329 xdup2(STDIN_FILENO, STDOUT_FILENO);
330
331 // Wait for initial server 220 message
332 smtp_check(NULL, 220);
333 }
334
335 // we should start with modern EHLO
336 if (250 != smtp_checkp("EHLO %s", host, -1))
337 smtp_checkp("HELO %s", host, 250);
338
339 // perform authentication
340 if (opts & OPT_a) {
341 smtp_check("AUTH LOGIN", 334);
342 // we must read credentials unless they are given via -a[up] options
343 if (!G.user || !G.pass)
344 get_cred_or_die(4);
345 encode_base64(NULL, G.user, NULL);
346 smtp_check("", 334);
347 encode_base64(NULL, G.pass, NULL);
348 smtp_check("", 235);
349 }
350
351 // set sender
352 // N.B. we have here a very loosely defined algorythm
353 // since sendmail historically offers no means to specify secrets on cmdline.
354 // 1) server can require no authentication ->
355 // we must just provide a (possibly fake) reply address.
356 // 2) server can require AUTH ->
357 // we must provide valid username and password along with a (possibly fake) reply address.
358 // For the sake of security username and password are to be read either from console or from a secured file.
359 // Since reading from console may defeat usability, the solution is either to read from a predefined
360 // file descriptor (e.g. 4), or again from a secured file.
361
362 // got no sender address? use auth name, then UID username as a last resort
363 if (!opt_from) {
364 opt_from = xasprintf("%s@%s",
365 G.user ? G.user : xuid2uname(getuid()),
366 xgethostbyname(host)->h_name);
367 }
368 free(host);
369
370 smtp_checkp("MAIL FROM:<%s>", opt_from, 250);
371
372 // process message
373
374 // read recipients from message and add them to those given on cmdline.
375 // this means we scan stdin for To:, Cc:, Bcc: lines until an empty line
376 // and then use the rest of stdin as message body
377 code = 0; // set "analyze headers" mode
378 while ((s = xmalloc_fgetline(G.fp0)) != NULL) {
379 dump:
380 // put message lines doubling leading dots
381 if (code) {
382 // escape leading dots
383 // N.B. this feature is implied even if no -i (-oi) switch given
384 // N.B. we need to escape the leading dot regardless of
385 // whether it is single or not character on the line
386 if ('.' == s[0] /*&& '\0' == s[1] */)
387 bb_putchar('.');
388 // dump read line
389 send_r_n(s);
390 free(s);
391 continue;
392 }
393
394 // analyze headers
395 // To: or Cc: headers add recipients
396 check_hdr = (0 == strncasecmp("To:", s, 3));
397 has_to |= check_hdr;
398 if (opts & OPT_t) {
399 if (check_hdr || 0 == strncasecmp("Bcc:" + 1, s, 3)) {
400 rcptto_list(s+3);
401 last_hdr = HDR_TOCC;
402 goto addheader;
403 }
404 // Bcc: header adds blind copy (hidden) recipient
405 if (0 == strncasecmp("Bcc:", s, 4)) {
406 rcptto_list(s+4);
407 free(s);
408 last_hdr = HDR_BCC;
409 continue; // N.B. Bcc: vanishes from headers!
410 }
411 }
412 check_hdr = (list && isspace(s[0]));
413 if (strchr(s, ':') || check_hdr) {
414 // other headers go verbatim
415 // N.B. RFC2822 2.2.3 "Long Header Fields" allows for headers to occupy several lines.
416 // Continuation is denoted by prefixing additional lines with whitespace(s).
417 // Thanks (stefan.seyfried at googlemail.com) for pointing this out.
418 if (check_hdr && last_hdr != HDR_OTHER) {
419 rcptto_list(s+1);
420 if (last_hdr == HDR_BCC)
421 continue;
422 // N.B. Bcc: vanishes from headers!
423 } else {
424 last_hdr = HDR_OTHER;
425 }
426 addheader:
427 // N.B. we allow MAX_HEADERS generic headers at most to prevent attacks
428 if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
429 goto bail;
430 llist_add_to_end(&list, s);
431 } else {
432 // a line without ":" (an empty line too, by definition) doesn't look like a valid header
433 // so stop "analyze headers" mode
434 reenter:
435 // put recipients specified on cmdline
436 check_hdr = 1;
437 while (*argv) {
438 char *t = sane_address(*argv);
439 rcptto(t);
440 //if (MAX_HEADERS && ++nheaders >= MAX_HEADERS)
441 // goto bail;
442 if (!has_to) {
443 const char *hdr;
444
445 if (check_hdr && argv[1])
446 hdr = "To: %s,";
447 else if (check_hdr)
448 hdr = "To: %s";
449 else if (argv[1])
450 hdr = "To: %s," + 3;
451 else
452 hdr = "To: %s" + 3;
453 llist_add_to_end(&list,
454 xasprintf(hdr, t));
455 check_hdr = 0;
456 }
457 argv++;
458 }
459 // enter "put message" mode
460 // N.B. DATA fails iff no recipients were accepted (or even provided)
461 // in this case just bail out gracefully
462 if (354 != smtp_check("DATA", -1))
463 goto bail;
464 // dump the headers
465 while (list) {
466 send_r_n((char *) llist_pop(&list));
467 }
468 // stop analyzing headers
469 code++;
470 // N.B. !s means: we read nothing, and nothing to be read in the future.
471 // just dump empty line and break the loop
472 if (!s) {
473 send_r_n("");
474 break;
475 }
476 // go dump message body
477 // N.B. "s" already contains the first non-header line, so pretend we read it from input
478 goto dump;
479 }
480 }
481 // odd case: we didn't stop "analyze headers" mode -> message body is empty. Reenter the loop
482 // N.B. after reenter code will be > 0
483 if (!code)
484 goto reenter;
485
486 // finalize the message
487 smtp_check(".", 250);
488 bail:
489 // ... and say goodbye
490 smtp_check("QUIT", 221);
491 // cleanup
492 if (ENABLE_FEATURE_CLEAN_UP)
493 fclose(G.fp0);
494
495 return EXIT_SUCCESS;
496}
497
generated by cgit at 2024-05-15 14:51:30 (GMT)